Airport lighting and traffic control system



Sept. 29, 1942- r. A. LOGAN ET AL 2,296,936

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Sept. 29, 1942- T. A. LOGAN ETAL 2,296,936

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INVENTORS' THOMAS A. LOGAN IMRE MOLNAR ATTORNEYS Sept. 29, 1942.

T. A. LOGAQN ET AL AIRPORT LIGHTING AND. TRAFFIC CONTROL SYSTEM Filed Sept. 16, 1959 Se/ecfor Link 895 TO 07776!" Se/ecior Links 9 Sheets-Sheet 8 INVENTORS THOMAS A. LOGAN IMRE MOLNAR ,M; M M

ATTORNEYS.

- take off in his airplane.

Patented Sept. 29, 1942 AIRPORT LIGHTING AND TRAFFIC CONTROL SYSTEM Thomas A. Logan and Imre Molnar, Chicago, Ill., assignors to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application September 16, 1939, Serial No. 295,344

40 Claims. (Cl. 177352) The present invention relates to airport lighting and tramc control systems.

An airport conventionally comprises a flying field having a plurality of airplane runways thereon, some of the runways being arranged in intersecting relationship with respect to other of the rlmways and in non-intersecting relationship with respect to still other of the runways. l1- lumination devices of some form are usually associated with the flying field for the purpose of lighting the runways when the flying field is not otherwise clearly visible; and occasionally tramc signals of some form are associated with the flying field for the purpose of governing airplane trafflc on the runways.

In prior systems of the type noted it is often diflicult for an airplane pilot to determine which one of several runways on the flying field is intended for his use as the several runways may be lighted more or less to equal intensities. Furthermore, crossing runways are frequently lighted, rendering it impossible for the airplane pilot to determine which of the conflicting runways is intended for his use. Also, it often occurs that a pilot in an airplane aloft desires the use of a runway on the flying field to land his airplane at the same time a pilot in an airplane on the flying field desires the use of a runway thereon to In this event, neither pilot may be positive that a runway is intended for his use, this confusion being further aggravated when several runways on the flying field are lighted simultaneously. Moreover, in systems of this type an airplane pilot is frequently uncertain as to the proper direction of take off or of landing 'upon a given runway on the flying field, this uncertainty being most acute to an airplanepilot aloft when the given runway on the flying field is lighted.

Accordingly, it is an object of the present invention to provide in an airport lighting system comprising a flying field having a plurality of airplane runways thereon and a plurality of illumination means individually associated with the runways, an improved arrangement for selectively controlling the illumination means.

Another object of the invention is to provide in an airport fighting system of the type noted, an improved arrangement for selectively controlling the illumination means, which is so connected and arranged that the control of the illumination means associated with conflicting runways is positively prevented.

'Another object of the invention is to provide in an airplane lighting system of the type noted,

a dispatcher station and improved apparatus thereat for selectively controlling the illumination means and for observing the response of the illuminating means to the control exercised thereover.

Another object of the invention is to provide in an airport lighting system of the type noted, improved numerical switching apparatus for selectively controlling the illumination means.

A further object of the invention is to provide in an airport traflic control system comprising a flying field having a plurality of airplane runways thereon and a plurality of tramc signaling means individually associated with the runways, an improved arrangement for selectively controlling the signaling means.

A further object of the invention is to provide in an airport traffic control system of the type noted, an improved arrangement for selectively controlling the traii'ic signaling means, which is so connected and arranged that the control of the traflic signaling means associated with conflicting runways is positively prevented.

A further object of the invention is to provide in an airport traflic control system oi? the type noted, a dispatcher station and improved apparatus thereat for selectively controlling the traflic signaling means and for supervising the control thereof.

Another object of the invention is to provide in an airport tramc control system of the type noted, improved numerical switching apparatus for selectively controlling the traflic signaling means.

The features of the present invention are illustrated as being incorporated in an airport comprising a flying field having a plurality of airplane runways thereon, some of the runways being arranged in intersecting relationship with respect to other of the runways and in non-intersecting relationship with respect to still other of the runways. Illumination means and groups of traflic signals are individually associated with the runways. More particularly, the illumination means associated with each runway comwith the opposite ends of the runway and the arrows being associated with the stretch of the runway. Further, the airport comprises a dispatcher station including apparatus for selectively controlling the illumination means and the traflic signals and for supervising the control thereof.

In accordance with one feature of the invention the system comprises a plurality of numerical selector links, means at the dispatcher station for selecting any one of the selector links for use and means including a signal transmitter at the dispatcher station operative to transmit numerical signals to the selected selector link for selectively controlling the operation thereof. Two trunks are individually associated with each runway, each of the trunks being accessible to each of the numerical switches. The group of trafiic signals is so connected and arranged that the two trunks individually associated with the associated runway are individually selected by the selected numerical switch in accordance with the direction of airplane trafiic on the runway.

The selected selector link comprises means operative in response to any numerical signal to test the selection marking of acorresponding one of the trunks associated with one of the runways,.means for causing the selected selector link to select the one trunk in the event it is tested as not marked against selection, and means controlled by the selection of the one trunk for marking the one trimk against selection.

Further, the selected selector link comprises means for marking against seizure the other of the trunks associated with the other of the runways arranged in intersecting relationship with respect to the one runway. means controlled by the selection of the one trunk for testing the seizure marking of the one trunk and means for causing the selected selector link to seize the one trunk in the event it is tested as not marked against seizure. Also, each of the trunks comprises a plurality of control circuits adapted to be controlled to govern the illumination means associated with the associated runway and selectively to govern the group of tramc signals associated with the associated runway. Further,

the dispatcher station comprises means operative selectively to govern the control circuits in a selected one of the trunks.

In accordance with another feature of the invention the dispatcher station comprises a model fiying field including a plurality of illumination indicator means and a plurality of signal indicator means individually associated with the runways on the model flying field, and automatic means controlled when the illumination means and the trafllc signals associated with one .of the runwayson the flying field are governed for similarly governing the illumination indicator means and the signal indicator means associated with the corresponding runway on the model v flying field.

In accordance with a further feature of the invention the traflic signals associated with each inclusive, forairplane trafiic.

indication or the non-landing indication and the established directional take ofl. indication or the nonlanding indication and the non-take-ofl' indication.

In accordance with a further feature of the invention the group of trafilc signals associated with each of the runways on the flying field comprises first and second traflic signals, each of the traffic signals beingvisible to an airplane pilot aloft and to an airplane pilot on the flying field and adapted to display two different indications. The first and second traffic signals are so connected and arranged that the direction of airplane traffic on the runway is, determined by the particular one of the signals displaying an indication and the assignment of the runway to the use of an airplane aloft or to the use of an airplane on the flying field is determined by the particular indication displayed by the one signal.

Further, the system comprises means for selecting the control circuits of either one of the signals associated with the runway and means for selectively governing the selected control circuits.

Further features of the invention pertain to the particular connection and arrangement of the circuit elements of the system, whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, to-

gether with further objects and advantages thereof, will best be understoodby reference to the following specification taken in connection with the accompanying drawings, in which Figure 1 illustrates diagrammatically an airport lighting and traffic control system embodying the present invention; Fig. 2 illustrates diagrammatically an indicator panel incorporated in the system: Fig. 3 illustrates diagrammatically a control panel incorporated in the system; and Figs. 4 to 9, inclusive, taken together, illustrate diagrammatically the details of the control apparatus incorporated in the system.

cross pattern upon the flying field. Further, the

flying field is provided with a paved rectangular I boundary way communicating with each of the runway on the flying field comprise signaling Y means visible to an airplane pilot aloft and to an airplane pilot on the flying field; the signaling means being adapted to display non-landing and two different directional landing indications and non-take-ofl" and two different directional take off indications. Also, the system comprises means for preconditioning the circuits for controlling the signal means in order to establish the particular directional indications to be dis- P ayed by the signaling means and means for .selectively controlling the circuits. whereby the signaling means displays the established directional landing indication and the non-take-ofl runway ends in order to facilitate movement of the airplanes from the hangers to the various runway ends.-

The general boundary of the flying field Hill is outlined by a number of boundary lamps indicated at I03; while all elevated structures dis- Posed adjacent the boundary of the flying field are provided with hazard lamps indicated at I, Also, fiood'lamps indicated at I,- il'2, H3

and 4 are disposed substantially at the corners of the boundary of the flying field for general illumination purposes. Further, a revolving beacon indicated at H1 is associated with the flying field I00 for the purpose of. marking each runway are provided with rows of flushtype contact lamps in order to mark the boundaries'thereof. For example, the margins of the runway R4-RI2 are provided with rows of contact lamps indicated at I20. 1

In order to control airplane trafllc upon the runways, each runway end is provided with an arrow and a target, the arrow being of the flush type, visible to an airplane aloft, and the target being of the elevated type, visible only to an airplane on the flying field. For example, the runway ends RI, R4, RI2 and RI5 are provided respectively with arrows ARI, AR4, ARI2 and ARI5 and targets TRI, TR4, TRI2 and TRIS. Preferably, each of the arrows is substantially identical to the arrow ARI5, which comprises a red lamp I2I and a green lamp I22 disposed A therein; while each of the targets is substantially identical to the target TRIS, which comprises a red lamp I23, an amber lamp I24 and a green lamp I25 disposed therein.

In order to control the illumination of the common apparatus comprising the revolving beacon I", the flood lamps III, H2, H3 and H4, the T lamps II 5, the boundary lamps I03, the hazard lamps I04, and the gate lamps and selectively to control the various arrows and targets individually associated with the runway ends, control apparatus I02 is provided in the dispatcher control tower IOI. Also, there are provided in the dispatcher control tower IN a control panel 300 and an indicator panel 200, the control panel 300 being arranged to govern the control apparatus I02 and the indicator panel 200 being arranged to indicate illumination of the runways and the settings of the various arrows and targets associated with the runway ends. Preferably, the control panel 300 is disposed in a substantially horizontal position on the top of the desk of the dispatcher, while the indicator panel 200 isdisposed in either an inclined or a vertical position in front of the desk of the dispatcher, so that the dispatcher may readily operate the apparatus on the control panel 300 and observe upon the indicator panel 200 the illumination of the runways and the settings of the arrows and targets associated with the runway ends on the flying field I00.

Referring now to Fig. 2, the illustrated indicator panel 200 comprises an opaque sheet which is cut out and covered with translucent material in order to provide a general crisscross pattern corresponding precisely to the crisscross pattern of the runways on the flying field I00. Also, the ends of the various strips of translucent material carry a number of characters RI to RI8; inclusive, identifying the corresponding runway ends on the flying field, a number of arrows ARI cator panel which are adapted .to be illuminated in accordance with the illumination of the contact lamps disposed along the margins of the corresponding runway on the flying field. For example, the series of lamps 210 are disposed below the strip of-tran'slucent material on the indicator panel corresponding to the runway R5--RI5. Red and green lamps are disposed below each of the arrows carried by the translucent strips on the indicator panel which are adapted to be illuminated in accordance with the illumination of the red and green lamps in the arrows associated with the corresponding runway ends on the flying field. For example, the arrow ARI5 carried by the end RI5 of the translucent strip on the indicator panel has disposed therebelow a red lamp 2' and a green lamp 212. Red, amber and green lamps are disposed below each of the'targets carried by the translucent strips on the indicator panel which are adapted to be illuminated in accordance with the illumination of the red, amber and green lamps in the targets associated with the corresponding runway ends on the flying field. For example, the target TRIS carried by the end RI5 of the translucent strip on the indicator panel has disposed therebelow a red lamp 213, an amber lamp 214 and a green lamp 215.

Further, the indicator panel 200 comprises three groups of pilot lamps individually corresponding to three selector links included in the control apparatus I02. Each group of pilot lamps comprises eighteen pilot lamps individually corresponding to the eighteen runway ends on the fiying field. For example, the first group of pilot lamps individually associated with the first selector link in the control apparatus I02 comto ARI8, inclusive, identifying the corresponding arrows associated with the runway ends on the flying field, and a number of targets TRI to TRI8, inclusive, identifying the corresponding targets associated with the runway ends on the fly ng field. A series oflamps are disposed below each of the translucent strips on the indiprises the pilot lamps 20I to 2I8, inclusive, which respectively correspond to the runway ends RI to RI8, inclusive. Similarly, the first pilot lamp 22I in the second group of pilot lamps individually associated with the second selector link in the control apparatus I 02 is individually associated with the first runway end RI; while the first pilot lamp 2 in the third group of pilot lamps individually associated with the third selector link in the control apparatus I02 is individually associated with the runway end RI. It is noted that when one of the selector links in the control apparatus I02 is operated to select one of the runway ends on the flying field, the pilot lamp corresponding to the selected runway end in the group of pilot lamps corresponding to the selected link utilized is illuminated. Accordingly, the illumiticular runway end which has been selected by a particular selector link in the control apparatus I02. 7

Referring to Fig; 3, the control panel 300 comprises three groups of keys individually corresponding to the three selector links in the control apparatus I02. For example, the first group of keys comprises the illustrated keys IKI, IK2 and IK3; the second group of keys comprises the illustrated keys 2KI, 2K2 and 2K3; while the third group of keys comprises the illustrated keys 3KI, 3K2 and 3K3. Preferably, the three keys in each of the three groups of keys are connected and arranged to perform similar functions in the respective selector links in the control apparatus I02. For example, the key IKI comprises a select-release key for the first selector link; the key IK2 comprises a take ofi-land-emergency stop key for the first selector link; while the key IK3 comprises a traific on-ofl-runway and trafflc on key for the first selector link.

Also, the control panel 300 comprises a group of common keys, including the keys KI to KI 0, inclusive, the keys KI to K6, inclusive, being arranged to control the illumination of the gate lamps associated with the gates I to 0, respectively; the key K1 being arranged to control. the illumination of the boundary and hazard lamps; the key K8 being arranged to control the illumination of the T lamps; and the key K3 being arranged to control the illumination of the revolving beacon. Finally, the key KIO is arranged to control the intensity various runways on the flying field. More particularly, by manipulating the key KIII the illumination of the contact lamps disposed along the margins of the various runways on the flying field may be varied to three diflerent intensities; namely, normal, dim and bright. Further, a group of pilot lamps 3 to 3I9, inclusive, is provided on the control panel 300 and individually associated with the keys KI to K9, respectively, these pilot lamps being so connected and arranged that they are illuminated in accordance with the bperation of the respective keys. Also, four keys KI I, KI2, KI3 and KI4 are provided on the control panel for the purpose of controlling the illumination of the respective flood lamps I I I, H2, H3 and I I4. Further, there is provided on the control panel a push button pattern 340 which corresponds precisely to the general criss-cross pattern of the runways on the flying field. Also, the push button pattern 340 comprises eighteen push buttons PRI to PRI8, inclusive, respectively positioned on the pattern 340 in accordance with the positions of the various runway ends on the flying field. More particularly, each of the push buttons is connected and arranged in such a manner that it is operative, when depressed, to cause the amber lamp in the target associated of illumination of the contact lamps disposed along the margins of the with the corresponding runway end on the flying field to flash and to cause the amber lamp in the target associated with .the corresponding end of the translucent strip on the indicator panel to flash. For example, when the push button PRI5 is depressed, theamber lamp I 24 in the target TRI5 associated with the corresponding runway end R15 on the flying field is flashed and the amber lamp 214 in the target TRI5 associated with the corresponding end R I 5 of the translucent strip on the indicator panel is flashed.

Finally, the control panel 300 is provided with a number dial 30I comprising a rotatable finger disk 302 and a finger stop 303, this number dial being of the usual automatic telephone type. The number dial 30l is so connected and arranged that it is operative to control a selected one of the selector links inthe control apparatus I02 in order to cause the selected selector link to select any desired one of the runways on the flying field for the purpose of governing the illumination of the contact lamps disposed along the margins of the selected'runway and the settings of the signals individually associated with the opposite ends thereof.

Referring now to Figs. 4 to 9, inclusive, the control apparatus I02 comprises certain common equipment associated with the common keys KI to KIO, inclusive, on the control panel 300 and withthe three selector links, an impulse receiver unit I00 commonly'associated with the three groups of keys on the control panel, and

' 300, the gate three selector. links commonly associated with 7 the impulse receiver unit, the first selector link being indicated at 035.

This common equipment comprises a stepdown transformer 445, having a primary winding 445 connected by way of a control switch $400 to a source of low voltage A. 0. supply 401, and a secondary winding 441 included in the various control circuits governed by the keys on the control panel 300. Also. this common equipment includes a power transformer ill having a primary winding arranged in three sections 6, H2 and M3, and a secondary winding ill, and two choke coils H5 and H0. The various series of contact lamps I20, 635, 630, etc., disposed along the marginsof the runways on the flying fleld, are adapted to be respectively connected across the secondary winding 6 of the power transformer 0I0 by a number of slave relays R620, R622, R624, etc.; while the various sections of the primary winding of the power transformer 6I0 are adapted to be connected in a predetermined manner to a source of high voltage A. 0. supply 00I by a control switch S502 and three'two-pcsition switches S520 and S530. Each of the two-position switches S5l0, S520 and S530 is of the heavy duty, double acting, solenoid type, comprising operating and releasing windings. A circuit network is provided for controlling the operating and releasing windings of the two-position switches S5I0, S520 and S530, which comprises three switch control relays R4I0, R4I5 and R420, three lockout relays R425, R430 and R435, and a control relay R450.

Further, the common equipment comprises a group of six gate relays, including the gate relay R550; a group of six gate slave relays, including the gate slave relay R5501 a group of eighteen target relays, including the target relay R540; and a group of eighteen target slave relays, including the target slave relay R555. It is noted that the gate relays are individual to the respective gates associated with the flying field, the gate relay R550 being individual to the first gate and being operative to complete a circuit for energizing the gate lamps II 5 assoeiated with the first gate; while the target relays are individual to the respective targets assor ciated with the runway ends on the flying field, the target relay R540 being individual to the target TR5 associated with the runway end R5 on the flying field and being operative to complete a circuit for illuminating the amber lamp I30 in the target TR5. Each, of the circuits for illuminating the amber lamps in the various targets includes a flasher in order to cause the amber lamp to flash, the circuit for illuminating the amber lamp I30 in the target TR5 including the flasher 553. Also, this common equipment includes a boundary and hazard relay R545 and an associated boundary and hazard slave relay R555, the boundary and hazard relay R545 being operative to complete the circuits for illuminating the boundary and hazard lamps I03 and I04.

It is noted that the gate slave relays are arranged to control the illumination of the group of pilot lamps disposed on the control panel slave relay R550 being arranged to control the illumination of the first pilot lamp 3 in this group of pilot lamps. The boundary and hazard slave relay R555 is arranged to control the illumination of the pilot lamp 3" in the group of pilot lamps on the control panel 300; while the target slave relays are arranged in the various targets associated with the miniature runways on the indicator panel 200, the target slave relay R585 being arranged to control the illumination of the amber lamp 215 in the target TR associated-with the miniature runway end R5 on the indicator panel.

Further, the common equipment comprises a group of eighteen take ofi relays accessible to each of the selector links and individually corresponding to the eighteen runway ends on the flying field, this group including the take oiI relay R900 individually associated with the runway end RI2; a group of eighteen land relays accessible to each of the selector links and individually corresponding to the eighteen runway ends on the flying field, this group including the land relay R905 individually associatedwith the runway end RI2; a group of eighteen emergency stop relays accessible to each of the selector links and individually corresponding to the eighteen runway ends on the flying field, this group including the emergency stop relay R9I0 individually associated with the runway end RI2; and a group of nine contact lamp relays accessible to each of the selector links and individually corresponding to the nine runways on the flying field, this groupincluding the contact lamp relay R9 I5 individual to the runway R4RI2.

- It is noted that the various take off, land and emergency stop relays control the illumination of the red and green lamps in the targets and arrows associated with the various runway ends on the flying field; while the various contact lamp relays control the illumination of the vari-,

ous series of contact lamps disposed along the margins of the various runways on the flying field. For example, the take oil relay R900 is arranged to control the illumination of the red. lamp I44 in the arrow ARI2 associated with the runway end RI2, the illumination of the green lamp I41 in the target TR4 associated with the runway end R4, and'the illumination of the green lamp I62 in the target TRI2 associated with the runway end RI2; the land relay R905 is arranged to control the illumination of the red lamp I40 in the target TRI2 and the illumination of the green lamp I43 in the arrow ARI2; the emergency stop relay R9I0 is arranged to control the illumination of the red lamp I44 in the arrow ARI2, the red lamp I40 in the target TRI2, and the red lamp I45 in the target TR4: and the contact lamp relay R9I5 is arranged to control the energization of the slave relay R620, thereby to control the illumination of the series of contact lamps I20 disposed along the margins of the runways R4-RI2 on the flying field..

Also, the common equipment comprises a group of eighteen slave relays, including the slave relays R980 and R950, for controlling the illumination ofthe red lamps in the various targets associated with the miniature runway ends on the indicator panel, the slave relays R930 and R950 being arranged to control the illumination of the red lamps 283 and 290, respectively, in the targets TRI2 and TR4; a group of eighteen slave relays, including the slave relays R925 and R945, for controlling the illumination of the green lamps in the various targets associated with the miniature runwayends on the indicator panel, the slave relays R925 and R945 being arranged to-control the green lamps 285 and 288, respectively, in the targets TR.I2 and TR4; a group oi eighteenslave relays, including the slave'relay R940, for controlling the illumination of the red lamps in the various arrows associated with the miniature runway ends on the indicator panel, the slave relay R940 being arranged to control the red lamp 282 in the arrow ARI2; a group of eighteen slave relays, including the slave relay R995, for controlling the illumination of the green lamps in the various arrows associated with the miniature runway ends on the indicator panel, the slave relay R935 being arranged to control the green lamp-28I in the arrow ARI2; and a group of nine slave relays, including the slave relay R920, for controlling the illumination of the series of lamps disposed below the translucentstrips on the indicator panel, the slave relay R920 being arranged to control the illumination of the series of lamps 215 disposed below the translucent strip R4--RI2 on the indicator panel.

The impulse receiver unit comprises a rotary switch $180, including three wipers 18l, 183 and 185 provided with individually associated contact banks 182, 184 and 186 and a magnet M for simultaneously driving the wipers noted into engagement with the contacts in the associated contact banks. Also, a set of switch springs S1I8 is operatively associated with the wipers noted of the rotary switch S and arranged to be operated into engagement when the wipers of the rotary switch are operated away from their normal positions. Further, the im pulse receiver unit 100 comprises a start relay R140, a hold relay R150, a test relay R130,,a switching relayR150, a slave relay R190 and a circuit network.

Preferably, each of the'selector identical with the illustrated first selector link 895,

which comprises a rotary switch S800 including.

five wipers 80I, 803, 805, 801 and 809 provided with individually associated contact banks 802, 804, 805, 808 and 8I0 and a magnet M880 for driving the wipers noted into engagement with the contacts in the associated contact banks. Also, the selector link 895 comprises arotary switch $820 including five wipers MI, 823, 825,

821 and 829 provided with individually associated contact banks 822, 824, 826, 828 and 830 and a magnet M885 for driving the wipers noted into engagement with the contacts in the associated contact banks. Further, the selector link 895 comprises a test relay R850, a lockout-relay R840, nine marking relays including the marking relay R890, which individually corresponds to the nine runways, a stop relay R860, a switch-through relay R810 and a circuit network. Also, it is noted,

. trol system, a brief explanation of the method of controlling the signals associated with the opposite ends of the various runways on the flying field in order to coordinate the movements of diilerent airplanes is set forth below.

In order to control the take oi! of an airplane from the flying field I80 the dispatcher in the dispatcher control tower III first determines in accordance with the direction-oi the prevailing wind the particular runway which is to be utilized by the airplane in taking oil and the direction of take oil! on the runway and then views the yin field and the indicator panel 200 in order to satisfy himself that the flying field is clear as far as the determined runway is concerned. The dispatcher then selects the particular one of the three selector links which is to be utilized by operating the select keyon the control panel 300 corresponding to the selected link. The dial 30l on the control panel is then operated to cause the selected link to select the determined runway. After the determined runway has been selected, the dispatcher operates the take ofl! key of the selected link on the control panel, thereby to cause the signals associated with the opposite ends of the selected runway to be set in a predetermined manner. More particularly, the target associated with the near end of the selected runway displays a green light; the target associated with the remote end of the selected runway displays a green light; and the arrow associated with the near end of the selected runway displays a red light. The display of the green light by the near target indicates to the pilot in the airplane that he may safely taxi his airplane upon the near end of the selected runway; the display of the green light by the remote target indicates to the pilot in the airplane that his airplane may proceed along the selected runway and take oil; while the display of the red light by the near arrow indicates to a pilot in an airplane aloft that the selected runway is in use and that he may not safely land his airplane thereupon.

In order to control the landing of an airplane upon the flying field I the dispatcher in the dispatcher control tower l0| proceeds to select one of the runways with a selected one of the links in the previously described manner, and then operates the land key of the selected link on the control panel, thereby to cause the signals associated with the opposite ends of the selected runway to be set in a different predetermined manner. More particularly, the target associated with the near end of the selected runway displays a red light, the target associated with the remote end of the selected runway is dark, and the arrow associated with the near end of the selected runway displays a green light. The display of the red light by the near target indicates to a pilot in an airplane on the ying field that the selected runway is in use and that he may not safely taxi his airplane upon the near end of the selected runway; and the darkened condition of the remote target indicates to a pilot in an airplane on the flying field that the selected runway is in use and that he may not safely take off thereon; while the display of the green light by the near arrow indicates to the pilot in the airplane aloft that the selected runway is in readiness for use to land his airplane thereupon.

a y. dispatcher control tower "I, after selecting a runway on the flying field for the use of either an airplane which is to take ofl. thereupon or an airplane which is to land thereupon, may block the actual use of the selected runway by operating the emergency stop key of the selected link I on the control panel, thereby to cause the signals associated with the opposite ends of the selected runway to be set in a further predetermined manner. More particularly, the near target dis- .plays a red light, the remote target displays a it is noted that the dispatcher in the light. The display'of the red light by the near target indicates to a pilot in an airplane on the flying field that he may not safely taxi his airplane upon the near end of the selected runway; the display of the red light by the remote target indicates to a pilot in an airplane upon the near end of the selected runway that his airplane may not safely take oil thereupon; while the display of the red light by the near arrow indicates to a pilot in an airplane aloft that he may not safely utilize the selected runway to land his airplane.

In order to conserve time in the handling of airplane traiflc, the dispatcher may utilize the push button pattern 340 on the control panel 300, thereby to cause the target associated with any one of the runways to display a flashing amber light. This may be accomplished merely by depressing the particular push button on the push button pattern 340 corresponding to the target associated with the desired runway end on the flying field. This facility is utilized particularly in directing airplanes ofl of the flying field after they have landed on a selected one of the runways. For example, assuming that an airplane has landed on the runway end RI! of the flying fleld'and is taxiing toward the center intersection, the dispatcher in the dispatcher control tower i0! may operate the push button PR5 on the push button pattern 340 corresponding to the target TR5 associated with the runway end R5 on the flying field, thereby to cause the target TRS to display a flashing amber light. The display of the flashing amber light by the target TRS indicates to the pilot in the airplane taxiing along the runway end R12 toward the center intersection that he is to turn into the runway end R5 upon reaching the center intersection, thereby to clear the runway end RI! for the use of other airplanes.

Further, it is noted that the control apparatus I02, the signals on the flying field I00 and the indicator panel 200 are so connected and arranged that, when the dispatcher controls at the control panel 300 the signals associated with the opposite ends of any one of the runways on the flying field to display predetermined indications, the signals associated with the opposite ends of the corresponding runway on the miniature pattern of the flying field on the indicator panel 200 are controlled to display like indications. Accordin y, the signals displayed on the minature pattern of the flying field on the indicatonpanel 200 always correspond to the actual signals displayed on the flying field.

Considering now the operation of the control prevailing wind on the flying field a particular red light, and the near arrow displays a red one of the runways on the flying field for use and the direction of airplane traflic thereon, he selects one of the selector links to be utilized to select the, determined runway, as previously noted. Assuming that the dispatcher selects the first selector link 895 to be-utilized to select the determined runway on the flying field, this is accomplished by operating the key IKI on the control panel 300 to its select position. When the key IKI is operated to its select position, a circuit is completed, at the contacts 124 thereof,

,for energizing in series the upper and lower windings of the'lockout relay R840. This circuit extends from ground by way of the contacts 124 .of the key IKI, C; the upper winding of R840,

the contacts 852, the lower winding of R840 and ergizing the winding of the magnet M135 of the the resistor 015 to battery. It is noted that the point between the terminal of the lower winding of the lookout relay R040 and the resistor 015 is multipled to the other selector links. Accordingly, the upper and lower windings of the lockout relay R340 are sufllciently energized to cause this relay to operate only in the event the keys corresponding to the key IKI in the other selector links occupy their normal positions. Assuming that the above-mentioned condition prevails in the second and third selector links, the

upper and lower windings of the lookout relay rotary switch S100, to complete, at the contacts 152, an obvious path for applying battery potential by way or the resistor 110 to the conductor R040 are sufliciently energized .at this time in order to cause the lookout relay R840 to operate. Upon operating, the lookout relay R040 completes, at the contacts I, an obvious holding circuit for energizing the upper winding thereof and an obvious path for short-circuiting the lower winding thereof, thereby to retain the lookout relay R840 in its operated position and to load the resistor 015. when the resistor 815 is thus loaded by the lookout relay R0 in the first selector link 305, there is not adequate potential between ground and the multiple point to the lockout relays in the second and third selector links to permit operation of the lookout relays in these Accordingly, the second.

and third selector links cannot be utilized while the key lKl of the first selector link 805 occupies its select position. v

Also, upon operating, the lockout relay R000 1 prepares, at the contacts 842, a point in a circuit, traced hereinafter, for energizing the upper winding of the test relay R050, prepares at the contacts 843, a point in a circuit, traced here: inafter, for energizing the lower winding of the test relay R350, prepares, at the contacts 0, a point in a circuit, traced hereinafter, for energizing the winding of the magnet M000 of the rotary switch S300, interrupts, at the contacts 805, a point in a circuit, traced hereinafter, for energizing the winding of the magnet M005 of the rotary switch S020, and interrupts, at the contacts 046, a point in a circuit, traced hereinafter, for energizing the winding of the stop relay R380 and for illuminating the pilot lamp arranged in the first group of pilot lamps on the -indicator panel 266i and corresponding to the selected runway end on the flying field.

The dispatcher then operates the dial in accordance with the number of the determined runway end on the flying field by inserting his finger in the appropriate hold in the finger disk,

302 and then rotating the disk until his finger engages the finger stop 303. The finger disk 302 then returns to its normal position, thereby to cause the dial 301 to transmit a corresponding number of impulses. .When the dial 3" is operated away from its normal position the con-.

tacts 150 and 111 thereof are actuated into en-- gagement in order respectively to complete a path, traced hereinafter, for short-circuiting the winding of the test relay R130 and to complete a circuit for energizing the winding of the hold relay R150. The circuit for energizing the winding of the hold relay R150 extends from ground by way of the wiper 105 and engaged normal contact in the associated contact bank 135 of the rotary switch 8180, C100, the contacts 103, C130, the contacts 1" of the dial 50!, the contacts 120- of the key IKI, C133, the contacts 1, and the winding of R150 to battery. when energized over the above-traced circuit, the hold relay 1 R150 operates to prepare, at the contacts 15!,

a point in a circuit, traced hereinafter, for enafter, for energizing the lower winding of the switching relay R150.

After. the finger disk 302 of the dial 3 0l is released, the dial operates to transmit the corresponding number of impulses, as previously noted. More particularly, the contacts 1l5 of the dial 30l are operated into engagement and disengagement a number of times corresponding to the number of impulses to be transmitted. Each time the contacts "5 of the dial 30l are actuated into engagement, the previously mentioned circuit for energizing the winding of the magnet M135 of the rotary switch S180 is completed, assuming that the keys 2K| and 3'Kl individually associated with the second and third selector links occupy their normal positions. The

last-mentioned circuit extends from ground by way of' the contacts 161 of the key 3K1, C159, the contacts160 of the key IKI, C158,. the contacts 121' of the key IKI, C134, the contacts H5 of the dial 30l, C132, the contacts 15l and the winding of M135 to battery. Each time the above-traced circuit is completed, the magnet M135 operates to condition the wipers noted of the rotary switch $100 .to be driven one step in the clockwise direction; and each time this circuit is interrupted, the magnet M135 restores, thereby to cause the wipers noted of the rotary switch $180 to be driven one step in the clockwise direction. Also, each time the magnet M135 operof the magnet M135, as this relay is of the slowto-release type. In fact, the slave relay R100 does not restore until a short time interval following the final restoration of the magnet M135. Upon operating, the slave relay R190 completes, at the contacts 191, the previously mentioned path for short-circuiting the winding of the test relay R130, this path extending from ground by way of the contacts 19L the winding of R130, the contacts 142, G133 and the contacts 1" of the dial 30l to ground. Also, when the wipers noted of the rotary switch 5100 are operated away from their normal positions one step in the clockwise direction, the set of switch springs S113 is actuated into engagement, thereby to prepare an alternative circuit, traced hereinafter, for energizing the winding of the magnet M135, this circuit being retained interrupted at the contacts 122 of the key IKI at this time.

At the conclusion of the first digit the finger disk 302 of the dial 30! occupies its normal posif tion and the contacts H5, H6 and H1 of the dial 30l are operated into disengagement. Also, at this time,- the wipers noted of the rotary switch 8100 are operated away from their normal positions a predetermined number of steps corresponding to the digit transmitted'by the dial 301. When the contacts 111 ofthe dial 30] are actuated into disengagement. the previously traced circuit for energizing the winding of the hold relay R150 is this relay being of the slow-to-release type. Also, when the contacts "6 of the dial 30I are actuated into. disengagement the previously traced path for short-circuiting the winding of the test relay R130 is interrupted thereat. When the contacts 1I5 of the dial 30I are actuated into disengagement the previously traced circuit for energizing the winding of'the magnet M135 is interrupted. The subsequent operation of the test relay R130 depends upon several conditions, including the particular digit dialed as will appear hereinafter.

Assuming that the digit dialed at the dial 30! the digit 1, in this event the wipers noted of the rotary switch S180 are moved into engagement with the first contacts in the associated contact banks after the magnet M135 is deenergized. However, prior to'the restoration of the slave relay R100 and subsequent to the return of the finger disk 302 of the dial 30I to its normal position, a circuit is completed for'energizing the winding of the test relay R130 in the event the corresponding runway end RI on the flying field has not been previously selected by either the second or third selector links. This circuit extends from ground by way of the contacts 19I, the winding of R130, the contacts 142, C133, the contacts 152 and the resistor 119 to battery. When energized over the above-traced circuit, the test relay R130 operates to complete, at the contacts 13I, a circuit for energizing the lower winding of the start relay R140. This circuit extends from ground by way of the contacts 161 of the key 3KI, 0159,- the contacts 168 of the key 2KI, C158, the contacts 12I of the key IKI, the contacts 13I and the lower winding of R140 to battery. When energized over the above-traced circuit, the start relay R140 operates to complete, at

- the contacts 146, an obvious holding circuit for energizing the lower winding thereof. Also, upon operating, the start relay R140 interrupts, at the contacts 144, a further point in the previously traced holding circuit for energizing the winding of the hold relay R150 and prepares, at the contacts 145, a point in a circuit, traced hereinafter, for energizing the upper winding thereof. Further, the start relay R140 interrupts, at the contacts 142, a point in the previously traced circuit for energizing the winding of the test relay R130 and completes, at the contacts 143, an obvious path for applying battery potential by way of the resistor 119 to the conductor C133, and completes, at the contacts "I, an obvious path for applying ground potential to the conductor C110 for a purpose more fully described hereinafter.

Shortly after the magnet M135 restores, the slave relay R100 restores to interrupt, at the contacts I a further point in the previously traced interrupted thereat; however, the hold relay R150 does not immediately restore,

hereinafter, for energizing circuit for energizing the winding of the testrelay R130. Shortly after the previously traced holding circuit for energizing the winding of the hold relay R150 is interrupted, this relay restores to interrupt, at the contacts 15I, a further point in the previously traced circuit for energizing the winding of the magnet M135, to interrupt, at the contacts 152, a point in the previously traced original circuit for applying battery potential by way of the resistor 110 to the conductor C133, to interrupt, at the contacts 153, the previously mentioned path for applying ground potential to the conductor C138, and to is not completed when the dial 30I the switching relay R180.

At this time the wipers noted of the rotary switch S180 engage the first contacts in the associated contact banks as previously explained. Specifically, the wiper 185 of the rotary switch S180 engages the first contact in the associated contact bank 106, thereby to complete the previously mentioned circuit for energizing the lower winding of the switching relay R160, this circuit extending from ground by way of the wiper and engaged first contact in the associated contact bank 186, C140, the contacts 154 and the lower winding of R to battery. When energized over the above-traced circuit, the switching relay R160 operates to complete, at the contacts 166, a holding circuit for energizing the upper winding thereof, this circuit extending from ground by way of the contacts 161 of the key 3Kl, C159, the contacts 168 of the .key ZKI, C158, the contacts 12I of the key IKI, C151, the contacts 166 and the upper winding of R160 to battery. Also, upon operating, the switching relay R160 interrupts,

rotary switch S and the conductor C133, completes, at the contacts 162, an obvious connection between the wiper 183 of the rotary switch S180 and the conductor C133, interrupts, at the contacts 163, a further point in the previously traced original path for applying ground potential by way of the wiper 105 and engaged normal contact in the associated contact bank 106 to the conductor C138, and completes, at the contacts 164, an obvious alternative path for applying ground potential by way of the wiper 185 and engaged first contact in the associated con-' tact bank 186 to the conductor C138. 'Finally, the switching relay R160 prepares, at the contacts 165, a point in a circuit, traced hereinafter, for energizing the upper winding of the start relay R140. At this time tial is applied by way of the resistor 119, the contacts 152, the contacts 162, the wiper 103 and engaged first contact in the associated contact bank 104, C141 and the first conductor in the cable 116 to the first contact in the contact bank 802 of the rotary switch $800 in the first selector link 895. Also, the application of ground potential to the conductor C118 completes a cir- -cuit for initiating the operation of the first selector link 005 in a manner more fully described hereinafter.

In the foregoing description it was assumed that the runway end RI had not been previously selected by either the second orthird selector links when the Assuming now that when the digit 1 is dialed, the corresponding runway end RI has been previously selected by either the second or third selector links, the previously traced energizing the winding of the test is returned to its normal position. More particularly, in this event, when the dial 30I is returned to its normal position to interrupt, at the contacts 1I6 thereof, the previously traced path for shortcircuiting the winding of the test relay R130,.an alternative path for short-circuiting the winding of the test relay R130 is completed. This alterwinding of R130, the

complete-at the contacts 154, a circuit, traced 7 18I and engaged first contact, in the associated the lower winding of at the contacts 16l, an obvious connection between the wiper 18I of the battery potencorresponding digit 1 was dialed.

contact bank of the rotary switch $180 to the corresponding first conductor in the cable 116, the last-mentioned conductor in the cable 116, I

having ground potential appearing thereon in a manner more fully described hereinafter. Accordingly, at this time, the testrelay R130 does not operate. Hence, after the slave relay R190 that the first digit dialed at the dial 3 was the digit 1. Assuming now that the first digit dialed is some other digit other than 1 and any digit between 2 and 0, such, for example, as the digit 4, at the conclusion of the digit the finger disk 882 of the dial 30! is returned to its normal positioii, thereby to interrupt, at the contacts M6, the previously traced path for short-circuiting the winding of the test relay R130. At this time the wipers noted of the rotary switch S180 engage the fourth contacts in the associated contact banks and the previously traced circuit is completed for energizing the winding of the test relay R130 in the event the corresponding runway end R4 on the flying field has not been previously selected by either the second or the third selector links.. When thus energized, the

test relay R130 operates, as previously explained,

thereby to cause the start relay R140 to operate, whereupon operation of the first selector link 895 is initiated, as previously explained.

On the other hand, in the eventthe runway end R6 has been previously selected by either the second or third selector links, an alternative path for short-circuiting the winding of the test relay R130 is completed when the dial 38! is returned to its normal position. Accordingly, operation of the first selector link 895 is not initiated in this event, as previously explained.

In the foregoing descriptions it was assumed that only one digit was dialed at the dial 30!. Assuming now that two digits are to be dialed at the dial 30 i, the first digit comprising the digit 1 and the second digit comprising any digit between the digits 1 and 8, such, for example,

as the digit 2, a first digit 1 and a second digit 2 being dialed when it is desired to select the runway end RI2 on the flying field. At the conclusion of the first digit 1 the apparatus in the impulse receiver unit 100 occupies one of two conditions, depending upon whether the corresponding runway RI on the fiying field has been previously selected by either the second or third selector links, as previously explained.

Assuming that the runway end B1 on the flying field has not been previously selected by either the second or third selector links when the first digit 1 is dialed, the apparatus in the impulse receiver unit 100 occupies the condition initially explained and the finger disk 302 of the dial 30l is again actuated in accordance with the digit 2. In this event, when the finger disk 302 [of the dial. 30l is actuated away from its normal position, the contacts 1" in .the dial 30| are actuated into engagement, thereby to complete the previously mentioned circuit for energizing the upper winding of the start relay 164, C738, the contacts iii of the dial 30I, C156,

the contacts 120 of the key IKI, C139, the contacts 145 and 165 and the upper winding of R140 to battery. When the upper winding of the start relay R140 is energized over the abovetraced circuit, the lower winding thereof being energized by way of the previously traced holding circuit, the start relay R140 restores, this relay being of the differential type. Upon restoring, the start relay R140 interrupts, at the contacts 145, the previously traced circuit for energizing the upper winding thereof and interrupts, at the contacts 146, the previously traced holding circuit for energizing the lower winding thereof. Further, the start relay R140 completes, at the contacts 144, the previously traced circuitfor energizing the winding of the hold relay R150, thereby to cause the latter relay to operate. Also, the start relay R140 interrupts,

at the contacts 143, the previously traced alternative circuit for applying battery potential by way of the resistor 119 to the conductor C133, prepares, at the contacts 142, the previously traced path for short-circuiting the winding of the test relay R130, and interrupts, at the contacts "I, the previously mentioned path for applying ground potential to the conductor C118. Upon operating, the hold relay R150 completes, at the contacts 15L the previously mentioned circuit for energizing intermittently the winding of the magnet M135 of the rotary switch S180 by way of the dial 30L When the finger disk 302 of the dial 30l is released, the dial 3!" operatesto transmit a second series of impulses corresponding to the second digit, thereby to cause the magnet M135 to operate intermittently and drive the wipers noted of the rotary switch S180 a corresponding number of additional steps in the clockwise direc- R140, this circuit extending from ground by way of the wiper 185 and engaged first contact in the associated contact bank 186, C149, the contacts tion. At the conclusion of the second digit the wipers noted of the rotary switch S180 engage contacts in. the associated contact banks disposed one step in advance of the number of impulses included in thesecond digit. At the conclusion of the digit the finger disk 302 of the dial 30l is'returned to its normal position, thereby to interrupt, at the contacts 1I6, the previously traced path for short-circuiting the winding of the test relay R130. At this time the wipersnoted of the rotary switch S180 engage the third contacts in the associated contact banks and the previously traced circuit is completed for energizing the winding of the test relay R in the event the corresponding runway end RI2 on the flying field has not been previously selected by either the second or third selector links.

On the other hand, in the event the runway end-Rl2 has been previously selected by either the second or third selector links, an alternative l circuit is completed for short-.circuiting the winding of the test relay R130, this circuit extending from ground byway of the contacts 19! the winding of R130, the contacts 142, C133, the

, contacts 162, the wiper 183 andengaged' third contact in the associated contact bank 184 of the rotary switch S to the corresponding conductor in the cable 111, this conductor having ground potential appearing thereon in a manner more fully described hereinafter. Accordand the finger disk 302 of the dial 30l is again actuated in accordance with the digit 2. In this event, when the finger disk 302 of the dial 30! is actuated away from its normal position, the contacts 111 of the dial 30l are actuated into engagement, thereby to complete directly an alternative circuit for energizing the winding of the hold relay R150. This alternative circuit for energizing the winding of the hold relay R150 extends from ground'by way of the wiper 185 and engaged first contact in the associated contact bank 186 of the rotary switch S180, C149, the contacts 184, G138, the contacts 1" of the dial 30!, C158, the contacts 120 of the key IKI, C139, the contacts 144 and the winding of R150 to battery. When energized over the abovetraced circuit, the hold relay R158 operates as previously explained, thereby to render the magnet M135 operative in response to the additional digit transmitted by the dial 38 I. The subsequent operation of the impulse receiver unit 100 is the same as that previously explained, the operation of the impulse receiver unit 100 it is noted that,

at the conclusion of any digit or digits dialed at the dial 30I, the previously traced circuit for energizing the winding of the test relay R130 is completed only in the event the corresponding runway end on the flying field has not been previously selected by either the second or third selector links. On the other hand, in the event the corresponding runway end on the flying field has been previously selected by the second or third selector links, the previously traced circuit for energizing the winding of the rest relay R130 at the conclusion of the digit is not completed in view of the fact that an alternative circuit for short-circuiting the winding of thetest relay R130 is completed. As previously noted, this alternative circuit extends from ground by way of the contacts 19l, the winding of R130 and the contacts 142 to the conductor C133, from the conto the contact bank 802 of the rotary switch ductor C133 by way of the contacts 16! to the wiper 18l of the rotary switch S180, or from the conductor C133 by way of the contacts 162 to the wiper 183 of the rotary switch S180, the wiper 181 of the rotary switch S180 engaging acontact in the associated contact bank 182 having ground potential appearing thereon in the event the digit dialed comprises any digit between 1 and 0 and the wiper 183 of the rotary switch S180 engaging a contact in the associated contact bank 182 having ground potential appearing thereon in the event the digit dialed comprises any digit between 11 and 18. The ground potential appearing on the contact in the contact bank 182 engaged by the wiper '18l of the rotary switch S180 isderived by way of the corresponding conductor in the cable 118 from a contact bank in either the second or third selector linkscorresponding to the contact bank 802 of the rotary switch S800 in the first selector link 895, in the event the corresponding runway end on the flying field has been previously selected by the second or third selector links; and the ground potential appearing onthe contact in the contact bank 184 engaged by the wiper 183 of the rotary switch S180 is derived by way of the corresponding conductor in the cable 111 from a .contact bank in either the secondor third selector links corresponding S800 in the first selector link 885, in the event the corresponding runway end on the flying field has been previously selected by the second or third selector links. Accordingly, the test relay R130 in the impulse receiver unit 100 is not operated in the event the determined runway end on the flying field has been previously selected by either the second or third selector links. Hence, the start relay R140 in the impulse receiver unit .100 is not operated to initiate opera tion of the first-selector link 895 in this event.

Further, it is noted that, in the event the determined runway end has not been previously selected by the second or third selector links, the operation of the start relay R140 in the impulse receiver unit 100 is effective not only to initiate operation of the first selector link 895, but to mark with battery potential by way of the resistor 119 and the previously traced circuit a particular contact in the contact banks 182 or 184 of the rotary switch S180 corresponding to the determined runway end on the flying field. This marking of the contact in the contact banks 182 or 188 of the rotary switch S180 is efiective to control the operation of the first selector link 885 in a manner more iully described hereinafter. Also, it is noted that the impulse receiver unit 100 is so connected and arranged that it is responsive to a second digit after a first digit has been dialed only in the event the first digit dialed is the digit 1.

Continuing now with the operation of the first selector link 895 and assuming that the digits 1 and 2 have been dialed successively, the wipers noted of the rotary switch S180 engage the third contacts in the associated contact banks and the start relay R140 and the switching relay R180 occupy their operated positions. Accordingly, the third contact in the contact bank-184 engaged by thewiper 183 of the rotary switch S180 and corresponding to the twelfth contact in the contact bank 802 of the rotary switch S180 is -marked with battery potential, this marking path extending from battery by way of the resistor 118, the contacts 143, C133, the contacts 162, the wiper 183 and engaged third contact in the associated contact bank 184 of the rotary switch S180 and the corresponding conductor in the cable 111 to'the twelfth contact in the contact bank 802 of the rotary switch S800. Also, upon operating, the start relay R140 completes, at the contacts 14l, the previously mentioned path for applying ground potential to the conductor C118, thereby to initiate operation of the first selector link 895 as previously explained.

More particularly, this application of ground potential to the conductor C118 completes a circuit for energizing the lower winding of the test relay R850 and a multiple circuit for energiving the winding of the magnet M880 of the rotary switch S800. The circuit for energizing the lower winding of the test relay R850 extends from the grounded conductor C118 by way of the contacts 843, the resistor 811 and the lower winding of R850 to battery; and the circuit for energizing the winding of the magnet M880 extends from the groundedconductor C118 by way of the contacts 844, 855 and 88| and the winding of M880 to battery. When the lower winding of the test relay R850 is thus energized, this relay becomes extremely fast to operate when the upper winding thereof is energized. When the winding of the magnet M880 is thus energized, this magnet operates to interrupt, at the contacts 88I, the previously traced circuit forenergizing the winding thereof, thereby to cause themagnet M888 to restore and recomplete, at the contacts 88I, the previously traced circuit for energizing the winding thereof. Accordingly, the magnet M888 operates intermittently, thereby to cause the wipers noted of the rotary switch $888 to be driven step by step in the counterl pleted, this circuit extending from ground by way of the contacts 882, the upper winding of R858, C884 and the wiper 88I to the twelfth contact in the associated contact bank 882, this contact having battery potential appearing thereon. When the upper winding of the test relay R858 is thus energized, this relay operates exceedingly fast to interrupt, at the contacts 855, the previously traced circuit for energizing the winding .of the magnet M888, thereby to arrest further operation of the rotary switch 8888. Accordingly, at this time, the wipers noted of the rotary switch S888 engage the twelfth contacts in the associated contact banks.

Also, upon operating, the test relay R858, com pletes, at the contacts 854, an obvious path for short-circuiting the resistor 811, thereby to provide a low resistance holding circuit for the lower winding thereof. Further, the test relay R858 completes, at the contacts 858, an obvious path for applying direct ground potential to the conductor C854, thereby to mark with ground potential by way of the wiper 8M and engaged twelfth contact in the associated contact bank of the rotary switch $888 the corresponding conductor in the cable 111. This application of marking ground potential to the twelfth conductor in the cable 11! marks the corresponding runway end RI2 on the filying field against selection by either the second or third selector links. Also, upon operating, the test relay R858 interrupts, at the contacts 852, the previously mentioned path for short-circuiting the lower winding of the lockout relay R848, thereby to render the lockout relay R848 relatively fast to release when the key IKI is operated from its select position back to its normal position. Also, upon and prepares at the contacts 858, a circuit, traced hereinafter, for energizing the upper winding of the switch-through relay R818.

Also, the test relay R858 completes, at the contacts 851, a path for applying ground potential to the fourth contact in the contact bank 888 of the rotary switch S888, this path extending from ground by way of the contacts 851, C888, the wiper 884 and engaged twelfth contact in the associated contact bank 888 and C818 to the fourth contact in the contact bank 888 of the rotary switch S888. It is noted that ground potential is applied to the fourth contact in the contact bank 888 of the rotary switch $888 in view of the fact that the runway end R4 on the flying field is opposed to the determined runway end RI2 thereon. As previously noted, upon operating,

- the mar-king relay R888 applies ground potential to the fifteen conductors included in the cable 888, which conductors are terminated by the contacts I to 8, inclusive, 5 to II, inclusive, and I4 to I8, inclusive, in the contact bank 888 of the rotary switch $888, the runway end R3 being an opposing runway end to the determined runway end RI2 on the flying field and the runway ends RI, R2, R5 to RII, inclusive, and RM to RIB,

inclusive, being intersecting runway ends with respect to the determined runway end-RIZ. Accordingly, at this time, all of the contacts, with the exception-of the twelfth and thirteenth contacts in the contact bank 888 of the rotary switch S888 are marked with ground potential due to the fact that the runway end RI 2 is the deter ,mined runway end and the runway end RI3 is the only other runway end not conflicting with the determined runway end RIZ. noted that the marked contacts in the contact banks 882 and 888 of the rotary switch $888 in the first selector link 885 are multipled to corresponding contacts in the contact banks of corresponding rotary switches in the second and third selector links, thereby to prevent the second and third selector links from seizing trunks associated with conflicting runway ends on the flying field, as will be explained more fully hereinafter.

Finally, upon operating, the test relay R858 I prepares, at the contacts 858, a circuit for energizing the winding of the magnet M885 of the rotary switch $828, which circuit is completed when operating, the test relay R858 prepares, at the contacts 85I, an alternative holding circuit, traced hereinafter, for energizing the lower winding thereof and completes, at the contacts 858, a circuit for energizing the winding of themarking relay R888. The circuit for energizing the winding of the marking relay R888 extends from ground by way of the contacts 858, the wiper 888 and engaged twelfthcontact in the associated contact bank 884 of the rotary switch S888, and the winding of R888 to battery. when energized over the above-traced circuit, the marking relay R888 operates to complete, at'the contacts 88I,

882, etc., obvious paths for applying ground poin multiple with the pilot lamp m m the first group of pilot lamps on the indicator panel 288,

the dispatcher in the dispatcher control tower I8I returns the key IKI- of the first selector link 885 from its select position to its normal position. Before the dispatcher in the dispatcher control tower I8I returns the key -IKI from its select position to its normal position, he first operates the keys IK2 and IK3, the key IK2 being operated in accordance with the use to be made of the determined runway end RI! and the key IK3 being operatedin accordance .with the visual condition of the flying field. In the event the flyin fleld is clearly visible and illumination of the contact lamps disposed along the margins of the runway R4 RI2 is not required, the key IK8 is operated to its traflic-on position. On the other hand, in the event the flying fleld is not clearly visible and illumination of the contact lamps disposed along the margins of the runway R4-RI2 I is required, the key IK8 is operated to its runway and trafllc on position. v

Assuming that the flying field is clearly visible and that the determined runway RI! is to be used by an airplane taking oil, the key IK 8 is operated to its trafllc on position and the key I K! is retained in its take off position. After the keys IE2 and IK8 have been thus operated, the

Further, it is 

